1. Technical Field
The present invention is directed to the art of welding a stud to a workpiece and, more particularly, to improvements in a stud welding gun.
2. Prior Art
A typical stud welding system includes a power supply, control circuitry and a stud welding gun. Such a welding gun includes a gun body and a gun shaft. The shaft is mounted to the gun body for reciprocal movement with respect thereto between fully extended and fully retracted positions. The gun shaft has a distal end having means, such as a chuck, for carrying a stud to be welded to a workpiece. Typically, the gun is a hand held device and includes a member known as a foot which is fixed to and extends forwardly of the gun body and is placed up against a workpiece to which a stud is to be welded. Thereafter, the operator actuates a trigger which energizes an electric solenoid which causes the shaft to be retracted to a lift position while appropriate circuitry supplies welding current to the shaft and the stud. After an arc has been established, the control circuitry deactuates the solenoid and the shaft is driven by a spring so as to plunge toward and cause the stud to engage the workpiece, at which time welding therebetween takes place. An apparatus for accomplishing the foregoing is disclosed in the U.S. patent to P. A. Glorioso U.S. Pat. No. 5,030,815.
In my previous U.S. Pat. No. 5,070,226 there is disclosed a stud welding gun similar to that as described above but which does not employ a solenoid for lifting the gun shaft and a spring for, upon de-energization of the solenoid, causing the shaft to plunge toward the workpiece. Instead, that patent discloses a gun employing a rotary stepper motor interconnected between the gun body and the gun shaft. The motor has an associated rotary to linear converter which serves to drive the gun shaft relative to the gun body in forward and reverse directions. Thus, the shaft may be driven in a reverse direction to a lift position and thereafter driven in a forward or plunge direction to cause a stud to engage a workpiece to achieve a weld therebetween.
The prior art typically employs a foot on a hand held welding gun to assist in initially positioning the gun relative to a workpiece prior to commencing a welding cycle. If such a foot is not employed, as in an automatic welding machine system, difficulties may arise in initializing the system prior to a welding cycle. That is, a starting or reference position of the welding gun relative to the workpiece may be needed.
Moreover, the prior art described above does not provide for a linear motor for directly driving the gun shaft in forward and reverse directions. Instead, the welding gun disclosed in my aforesaid patent discloses a rotary to linear converter in conjunction with a rotary stepper motor for driving the shaft in forward and reverse directions.